[s-cars] ABS-OFF switch

[Igor Kessel]

Folks,
I have finally decided to retrofit the ABS-OFF switch into my '97 S6. 
Generally I used Fred's brilliant approach. The only difference was the 
donor switch. Fred used the Fog Light switch to bastardise and I used 
the Rear Defroster switch. In retrospect I wish I had used the Fog Light 
switch as well since it has a second indicator bulb which lights up when 
the switch is activated, but I couldn't find one in the U-Pull It yard 
that I scavenged.

However I ran into a peculiar problem, which is unique to my particular 
car. My car originally came with the digital metric-only Instrument 
Cluster. I replaced it with a mechanical cluster off a wrecked '94 S4 
when I brought the car into the country and federalised it for PennDOT. 
I also heavily modified this cluster by building in the 20-LED Lambda 
gauge, the WGFV LED and a voltmeter off my '97 cluster in place of the 
stupid clock. Oh' and since now I had the actual functioning oil 
pressure gauge in the older cluster, I also bought and installed a '91 
Audi 200 oil pressure sender into the plugged port in my car, ran a wire 
from the engine compartment, populated the empty position #2 in the 
black 4-pin plug and connected it to the cluster. So now on the right I 
have three real gauges. Can you say "Frankencluster"? :)

The '94 S4 cluster was a direct match for my '97 S6 and has worked 
perfectly well. Or so I thought up until yesterday. I retrofit the 
ABS-OFF switch along with the relay per Fred's Munro excellent colourful 
pictorial write-up in the Acrobat format. When I depress the switch OFF 
and back ON I can hear the ABS pump going through the initiation 
routine. However the ANTILOCK OFF signal lamp in the Instrument Cluster 
does not come on. Turns out that it never did. Not with the '94 cluster 
anyway. I never even noticed its absence on the initial start-up for all 
those years that I owned the car. The ABS worked fine thus I never even 
suspected anything.

I will leave out several hours of tracing the problem in the Bentley 
schematic diagrams. I discovered that in the '94 cluster one terminal of 
the ABS K47 signal lamp is connected to the bus 15 (+12v when the 
Ignition is ON), and the other terminal is connected to the pin #13 of 
the red T26 connector on the back of the cluster. However in the '97 
cluster one terminal of the ABS K47 signal lamp is still connected to 
the bus 15 (+12v when the Ignition is ON), yet and the other terminal is 
connected to the pin #19 of the red T26 connector on the back of the 
cluster. Lovely. In both clusters the corresponding wire in the plug is 
YEL/RED. Only the pin that it was connected to was different. Bizarre.

Just in case I checked the position #13 in the male plug of my '97 
harness. It was empty. The position #19 was populated with the proper 
YEL/RED wire.

Since I don't have a '94 S4 to test the harness I had to go by the 
Bentley manual. It states "#19 - NOT USED". So far so good.

I promptly opened up the cluster and soldered a jumper wire from pin #13 
to pin #19 on the PCB side of the red T26 female connector. Reassembled 
the cluster and installed it in my car. Turned the ignition ON and got 
the ANTILOCK OFF light. Finally! Started the car and discovered that the 
light failed to go out. Exercised the ABS-OFF switch and heard the 
unmistakable clicking of the ABS controller initiation routine. Strange.

That day I also installed the Low Beam rotary switch, which allows to 
dip my Xenons according to the number of passengers in the car. I 
decided to test this feature. When I turned the lights ON the ANTILOCK 
OFF light went out. And vise versa. This was getting stranger by the minute.

OK, back to the drawing board. I completely disassembled the cluster 
again, and painstakingly scraped the conforming coating off the PCB for 
the K47 bulb's track just to trace the damned thing. It turned out that 
although Mr. Bentley said "NOT USED" for the pin #19 in the '94 cluster, 
in actuality for some unknown reason the pin #19 was internally 
connected to the pin #22. Yes, you've guessed it right, the illumination 
dimmer circuit.

Exacto knife in hand, I cut the illumination circuit off pin #19. 
Reassembled the cluster again (are you counting, folks?) and connected 
it to the car. No more ANTILOCK OFF when I turn the lights on. Hell, no 
more ANTILOCK OFF light, period. Even with the ignition ON.

At this point I realised that I ought to start from the other end. The 
K47 bulb does indeed see +12v, since it sits on the common bus with the 
alternator's indicator light K2, and this one does come on when the 
ignition is ON. I guessed that the YEL/RED wire in the red K26 plug 
fails to provide the GND to the bulb when the ignition is turned ON. In 
order to test this theory I stuck a needle into position #19 in the plug 
and connected a test light to it. I connected the other end of the test 
light to +12v. Turned the ignition ON. The test light did not light up.

This YEL/RED wire goes to the J104 ABS controller via the blue plug #6ac 
in the Connector Station I under the dashboard. I guess my next step 
would be to check the continuity of this wire from the Instrument 
Cluster in the torpedo all the way to the ABS controller under the rear 
seat.

Before I start tearing the car apart, can some kind soul with a '95.5 S6 
tell me if the ANTILOCK OFF bulb does indeed illuminate when the 
ignition is turned ON and subsequently goes out when the car is started? 
I am hoping I didn't burn anything yet...

Thanks for listening, folks.

-- 
Igor Kessel
two turbo quattros